My battery is 10.5 years old, has carried me many thousands of miles and performs almost like new. I say almost, as recently I sent the battery off to Jimmy at Insat for a recell, we both were of the belief that a battery that old must be close to end of life. It didn't feel that way, but maybe I had grown to adapt to the change in performance. Started life at 16ah and Jimmy measured it at 14ah and promptly returned it as delivered.
We discussed how the battery had held up so well. The bike was originally used for a 20 mile round trip commute. but now mainly for leisure 60-80 miles a week March to October. I explained my charging routine which is in the main to charge fully after every ride and also that I use the bike for fitness, so put quite some effort in. Jimmy's view was that it was probably a combination of a good BMS not charging the battery to full charge and the fact that by putting a lot of effort in, the battery is under less load. Where we differed was that November through February when the bike is idle I still leave the battery fully charged.